In a magnetic recording tape cartridge 1 as shown in FIGS. 1 and 2 having a magnetic recording tape 3 wound around a pair of hubs 4, in order to facilitate smooth rotation of the hubs 4 and stable running of the recording tape 3, there are interposed slip sheets 5 in one gap between the inner surface of a top wall 1a of the tape cartridge 1 and the top end surface 3a of the roll of the magnetic recording tape 3 including the top end surface of the hubs 4 and in another gap between the inner surface of a bottom wall 1b of the tape cartridge 1 and the bottom end surface 3b of the roll of the magnetic recording tape 3 including the bottom end surface of the hubs 4.
In such a recording tape cartridge, gaps are defined respectively in width of about 0.5 mm. Since the slip sheets 5 are essentially adapted to fill up the gaps, it is desirable to give cushioning effect to the slip sheets 5, which are elastically brought into contact with the hub end surfaces and the tape edges. Thus, it is well known in the art to emboss the slip sheets 5 with various configurations of projections or ribs while curling the slip sheets 5 in a convex manner as shown in FIG. 5.
When thus provided with the projections or ribs and curled in a convex manner, the slip sheets 5 prevent swaying of the hubs 4 and vertical movement of the recording tape 3, thereby improving the state of winding of the recording tape 3 with respect to the hubs 4 and stabilizing the tape running.
However, there comes into question the configuration of the ribs to be embossed on the slip sheets 5. Depending on the selected configuration, the ribs might be flattened by repeated use, resulting in loss of their essential function. Further, since the frictional sound is raised by increase in frictional pressure of the slip sheets 5 against the hub end surfaces and the tape edges, the configuration of the ribs must be selected to reduce such frictional sound.
In an example of the conventional recording tape cartridge as shown in FIG. 1, the slip sheets 5 are provided with a plurality of projections P which are projectingly formed in a hollow hemispherical configuration over the entire surfaces thereof. Since the respective configurations are not linked with one another in such a construction, the ribs are liable to be flattened and thus it is difficult to maintain the cushioning effect of the slip sheets for a long period of time. It is well known in the art that the slip sheets are longitudinally curled in a convex manner as shown in FIG. 5 so that the central highest portions in the widthwise direction thereof are faced to the end surfaces of the hubs 4 and the end surface of the roll of the recording tape to further prevent swaying of the hubs 4 and vertical movement of the recording tape 3. However, when the projections P are embossed in a dotted manner on such curled slip sheets 5, only the central portions in the longitudinal and widthwise directions of the slip sheets 5 are apt to be reformed in convexly swollen forms, and the cushioning effect cannot be obtained at the peripheral portions of the slip sheets, and it is difficult to maintain and/or reinforce the curling of. the slip sheet. Such slip sheets are effective, though, in improving slidability and reducing the frictional sound since contact areas of the hub end surfaces and the tape edges with respect to the slip sheets are reduced particularly when the slip sheets are set in place with the surfaces of the ribs faced to the hub end surfaces and the tape edges.
Thus, ribs or projections to be embossed on the slip sheets 5 are preferably continuous in both longitudinal and widthwise directions over the entire surfaces of the slip sheets 5. For this purpose, there are proposed other slip sheets as shown in FIGS. 9 and 10 in which each of the rib units is formed in a triangular configuration 91 (see FIG. 9) or a rectangular configuration 92 (see FIG. 10) in plan view.
However, a series of triangular and/or rectangular ribs 91 and 92 in linear linkages of the ribs. Consequently, the slip sheets are subjected to creasing along the linking lines, to reduce strength of the ribs 9 themselves. Further, when the slip sheet 5 are curled in the aforementioned convex manner, the central portions in the longitudinal and widthwise directions of the slip sheets are apt to be convexly swollen similarly to those embossed with the hemispherical projections in a dotted manner, and likewise it is difficult to maintain and/or reinforce the curling characteristics. Still further, since the ribs 9 are continuous in a linear manner, the frictional sound is spread over the entire surfaces of the slip sheets, leading to increase of the frictional sound.